Conventionally, as an analytical technique employing electrophoresis, there have been performed analyses based on separation by slab gel using a polyacrylamide gel, agarose gel, or the like as a support for separation. The separation by slab gel has some defects such that its resolution is limited by factors such as temperature changes and pH changes during electrophoresis, and that it is unsuitable for analysis of trace samples and automation of devices.
A method for solving the defects includes capillary electrophoresis, which enables automated measurement of trace samples with suppressing the generation of temperature changes. However, the lower limit for the effective length of the existing capillary electrophoresis device is about 8 cm depending upon the construction of the device, so that there is actually a limitation on miniaturization of the device.
On the other hand, with the recent developments in microfabricated device techniques, various DNA analytical devices, including capillary electrophoresis devices have been miniaturized [Becker, H. et al., Electrophoresis, 2000, 21, 12–26; Ueda, M. et al., Anal. Scie., 2000, 16, 657–658; Simpson, P. C. et al., Proc. Natl. Acad. Sci. U.S.A., 1998, 95, 2256–2261; Backhouse, C. et al., Electrophoresis, 2000, 21, 150–156; Kopp, M. U. et al., Science, 1998, 280, 1046–104; Waters, L. C. et al., Anal. Chem., 1998, 70, 158–162; and Han, J. et al., Science, 2000, 288, 1026–1029]. Concretely, there have been provided by miniaturization techniques, for instance, a capillary array electrophoresis device [the above-mentioned Simpson et al., Proc. Natl. Acad. Sci. U.S.A.; the above-mentioned Backhouse et al., Electrophoresis], a PCR-chamber-integrated electrophoresis device [the above-mentioned Kopp, M. U. et al., Science; the above-mentioned Waters, L. C. et al., Anal. Chem.], and an entropic trap array (gel-free) electrophoresis device [the above-mentioned Han, J. et al., Science]. 
However, there are some defects in the miniaturization techniques such that, for instance, in order to carry out separation excellently under the steady electric field in the sample-separation process, a longer effective length is necessitated [the above-mentioned Han, J. et al., Science]. 
On the other hand, non-steady electric field methods such as electric field inversion method are means which have been performed in ordinary pulse field electrophoresis using agarose gel, and are in many cases used for separation of long-chain DNA of several dozen kilo-base pairs or more.
However, there are some defects in the above-mentioned non-steady electric field methods such that it is difficult to apply the methods to conventional capillary electrophoresis from the viewpoint that an expensive electric power source would be required for high-speed inversion of high electric field.